1. Field of the Invention
The present invention relates to a display device with a touch panel, an event switching control method performed in the display device, and a computer-readable storage medium that causes a computer to execute the event switching control method.
2. Description of the Related Art
Being available in the market are products so-called “electronic whiteboards” including a large size display having a size of about 40 inches to 60 inches such as a flat panel, e.g., a liquid crystal display and a plasma display, and one using a video projector, and a touch panel mounted on the display. When a personal computer is connected to these products, such products can project an enlarged image of a screen of the personal computer thus connected, and is used for purposes such as making presentations in a meeting. Usually, these products provide “a function for operating a personal computer via a touch panel” utilizing functions of the touch panel mounted on the product so that a user can touch a projected image of the screen directly to make operations on the computer having the screen image projected, instead of making operations with a mouse. Such equipment is also provided with electronic whiteboard application software running on the personal computer to be connected to the equipment. The application software provides “functions for allowing handwriting via a touch panel”, such as a function for providing a screen functioning as a whiteboard and allowing a user to handwrite letters and the like via the touch panel, and a function for capturing the screen image of the personal computer running the application and allowing the user to handwrite something over the image.
For a touch panel used in such an electronic whiteboard, an optical touch panel is often used for reasons that, for example, a large display, e.g., in a size of 50 inches, can be applied, and no film-like structure needs to be pasted on the display surface so that the image quality of a flat panel display such as a liquid crystal display and a plasma display does not deteriorate. One of characteristics of an optical touch panel is that “any pen-like stick or finger (hereinafter, referred to as a stylus) interrupting or reflecting light” can be used in touching or writing, as disclosed in Japanese Patent Application Laid-open No. 2008-176802, for example.
Such an optical touch panel determines whether a stylus is inserted into the display surface, that is, whether the stylus is brought into contact with the display surface based on whether the light (hereinafter, referred to as probe light) disposed near the display surface is interrupted or reflected by a predetermined amount during a process in which the stylus is inserted into the display surface. In other words, such a determination is made based on whether the light intensity detected by a given light receiving element reaches a predetermined threshold. When it is determined that the light intensity reaches the threshold, a touched position at that time is notified to the personal computer connected to the equipment by sending touched position information to the personal computer as a mouse event.
However, for several reasons, it is difficult, at every point across the entire display surface, to match the threshold and a position of the stylus tip in a direction perpendicular to the display surface at a moment that the stylus comes into physical contact with the display surface. The reasons include a precision in a mechanical arrangement of the light sources and the display surface, dispersion of the probe light, and dispersion of the image on the light receiving element caused by the system not always allowing the stylus to be imaged onto the light receiving element. Otherwise, extremely high mechanical precisions exceeding the practical level are required to match them.
Most conventional electronic whiteboards using an optical touch panel are designed with some margin added to the threshold, setting the threshold to a position slightly above where the stylus comes into a physical contact with the display surface. As a result, the touch panel determines that the stylus touches the display surface when the stylus is slightly above the display surface, from a position where the stylus comes into a physical contact with the display surface. A mouse event at the position is then issued.
In addition, many conventional electronic whiteboards are provided with a special stylus (hereinafter, a special pen) with a pressure sensor, for example, for detecting that the tip of the stylus is brought into physical contact with the display surface. When a special pen is used, touch coordinates are issued as a mouse event when the light is interrupted by the special pen and the pen tip comes into physical contact with the display surface and causes the pressure sensor installed at the pen tip to detect a predetermined pressure. In this configuration, coordinates are detected only when the pen tip comes into physical contact with the display surface.
As to the handwriting function via a touch panel, many electronic whiteboard applications provides a mode for drawing freehand lines or graphics objects (hereinafter, a draw mode) and a mode for deleting drawn freehand lines or graphics objects (hereinafter, an erase mode). A most popular method for switching these two modes is clicking on a menu or a button displayed in a toolbar.
Another known method is to provide the electronic whiteboard having a tray on which a pen and an eraser are placed and including a sensor for detecting that the pen and the eraser are placed on the tray, and to cause the system to determine that one of the pen and the eraser not detected by the sensor is held in hand, to switch to the draw mode when the pen is held in hand, and to switch to the erase mode when the eraser is held in hand.
Furthermore, Japanese Patent No. 4208681 discloses a technology for operating a draw mode and a personal computer in a manner described below. A drag length from a point where the pen comes into contact with the display to a point where the pen is removed from the display is measured. If the drag length measured while the draw mode is selected is longer than a threshold, the draw mode is continued. If the drag length is shorter, the mode is switched to an operation mode for allowing the personal computer to be operated. Switching from the operation mode to the draw mode is achieved by touching a button on a toolbar.
Therefore, there is a need for an electronic whiteboard capable of reducing the user's burden in switching events such as the draw mode and the erase mode of an electronic whiteboard application while operating the electronic whiteboard having a touch panel, and of eliminating the user's need to be aware of the current mode.